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Item An Accurate Illumination Model for Objects Coated with Multilayer Films(Eurographics Association, 2000) Hirayama, H.; Kaneda, K.; Yamashita, H.; Monden, Y.This paper proposes an accurate illumination model for rendering objects coated with multilayer films. Optical phenomenaof multilayer films are caused by reflection, refraction, interference, and absorption of light inside each layer of multiple films, and these physical phenomena are complicatedly related with each other. The proposed method calculates composite reflectance and transmittance of multilayer films, taking into account all the physical phenomena described above, and visualizes the optical phenomena caused by the multilayer films accurately. The illumination model proposed in the paper can handle both smooth surface and locally smooth rough surfaces. Several examples of objects coated with various kinds of films demonstrate the usefulness of the proposed method.Item Combining finite element deformation with cutting for surgery simulations(Eurographics Association, 2000) Nienhuys, Han-Wen; van der Stappen, A. FrankInteractive surgery simulations have conflicting requirements of speed and accuracy. In this paper we show how to combine a relatively accurate deformation model—the Finite Element (FE) method—and interactive cutting without requiring expensive matrix updates or precomputation. Our approach uses an iterative algorithm for an interactive linear FE deformation simulation. The iterative process requires no global precomputation, so runtime changes of the mesh, i.e. cuts, can be simulated efficiently. Cuts are performed along faces of the mesh; this prevents growth of the mesh. We present a provably correct method for changing the mesh topology, and a satisfactory heuristic for determining along which faces to perform cuts. The incision surface will be jagged; this problem is a subject of current research.Item Geometric Signal Processing on Polygonal Meshes(Eurographics Association, 2000) Taubin, G.Very large polygonal models, which are used in more and more graphics applications today, are routinely generated by a variety of methods such as surface reconstruction algorithms from 3D scanned data, isosurface construction algorithms from volumetric data, and photogrametric methods from aerial photography. In this report we provide an overview of several closely related methods developed during the last few yers, to smooth, denoise, edit, compress, transmit, and animate very large polygonal models.Item Geometric Modeling Based on Polygonal Meshesv(Eurographics Association, 2000) Kobbelt, Leif P.; Bischoff, Stephan; Botsch, Mario; Kähler, Kolja; Rössl, Christian; Schneider, Robert; Vorsatz, JensWhile traditional computer aided design (CAD) is mainly based on piecewise polynomial surface representations, the recent advances in the efficient handling of polygonal meshes have made available a set of powerful techniques which enable sophisticated modeling operations on freeform shapes. In this tutorial we are going to give a detailed introduction into the various techniques that have been proposed over the last years. Those techniques address important issues such as surface generation from discrete samples (e.g. laser scans) or from control meshes (ab initio design); complexity control by adjusting the level of detail of a given 3D-model to the current application or to the available hardware resources; advanced mesh optimization techniques that are based on the numerical simulation of physical material (e.g. membranes or thin plates) and finally the generation and modification of hierarchical representations which enable sophisticated multiresolution modeling functionality.Item Robust Polygons Clipping to Model Complex Objects(Eurographics Association, 2000) Segura, Rafael J.; Feito, Francisco R.One of the most important problems to solve in Solids Modelling is computing the boolean operations for solids (union, intersection and difference). In order to implement these three operations an algorithm to compute the intersection between faces is needed (polygons clipping). In the case of solids with planar faces there are many solutions, although most of them are valid only when the faces are convex. In this paper we present an algorithm to determine the intersection between polygons of any nature (concave or convex, manifol or non-manifold, with or without holes, etc.) based on the idea of simplicial coverings proposed by Feito 11. One of the advantages of this approach is the robustness of algorithms, since decompositions or complex operations that may alter the results obtained are not avoided. A very interesting application of this algorithm is the modelling of complex solids with this type of polygons as faces.Item Spreading of the cultural heritage by means of multi-configurable, low cost virtual reality techniques(Eurographics Association, 2000) Flores, J.; Arias, J.; Saavedra, S.; Varela, E.; Ferro, J. M.; Taboada, J.In the last few years, computer graphics techniques have been applied to preserve and promote the cultural heritage. In this first steps the bottleneck of these applications developed was the price of the hardware that limited the use of these tools to museums or exhibition rooms. Nevertheless, the fast increase of graphic capacity of the computers allows the development of high -quality complex applications which can be visualized in personal computers. This is completed by multidisciplinary research groups that focus their efforts on the most relevant aspect of the learning and presence sense in virtual environments. In this paper, an application of V.R. techniques to the promotion of heritage patrimony bases, in a PC platform, is presented. Focus has been put into high screen quality, multiple screen, multi-user, stereoscopic image, 3D sound and multisensorial environments as well as the high transportability, scalability and low price aiming at a quite widespread use of this hardware. The virtual reality application developed shows the old part of Santiago de Compostela, European City of Culture for the year 2000. The model of t he city is complex enough to prove that it is possible to use PC´s as visualization engine, over high quality and complex models.Item Volumetric Textures(Eurographics Association, 2000) Gonzalez Clua, Esteban W.; Dreux, MarceloThere are some types of nature elements that are adequately represented in Computer Graphics only through volumes. In order to visualize scenes with volumes, together with geometrical objects, it is necessary to make use of a hybrid rendering algorithm. However, the presence of volumetric elements heavily increases the visualization processing time, independently of the technique being used. This article presents a method that is being developed in order to reduce the volumetric rendering to a projection of a special texture on a geometric surface that surrounds the volume. This technique seems to be particularly efficient to volumes that represent nature elements, such as gases, clouds and smoke. It is possible, however, to extend the method to other types of volumetric objects.Item Efficient Evaluation of the Field Functions of Soft Objects Using Interval Tree(Eurographics Association, 2000) Min, Kyung-Ha; Lee, In-Kwon; Park, Chan-MoWe present an algorithm to evaluate the field function of a soft object efficiently. Instead of using a global field function that is defined by the sum of all local field functions, we consider only the set of local field functions that affects a point at which we want to evaluate the field function. To find the affecting local field functions efficiently, we exploit a data structure called interval tree based on the bounding volume of the component corresponding to the primitives (skeletons) of a soft object. The bounding volume of each component is generated with respect to the radius of a local field function of the component, threshold value, and the relations between the components and other neighboring components. The proposed scheme of field function evaluation can be used in many applications for soft objects such as modeling and rendering, especially in interactive modeling process.Item Interactive Vegetation Rendering with Slicing and Blending(Eurographics Association, 2000) Jakulin, AleksDetailed and interactive 3D rendering of vegetation is one of the challenges of traditional polygon-oriented computer graphics, due to large geometric complexity even of simple plants. In this paper we introduce a simplified image-based rendering approach based solely on alpha-blended textured polygons. The simplification is based on the limitations of human perception of complex geometry. Our approach renders dozens of detailed trees in real-time with off-the-shelf hardware, while providing significantly improved image quality over existing real-time techniques. The method is based on using ordinary mesh-based rendering for the solid parts of a tree, its trunk and limbs. The sparse parts of a tree, its twigs and leaves, are instead represented with a set of slices, an imagebased representation. A slice is a planar layer, represented with an ordinary alpha or color-keyed texture; a set of parallel slices is a slicing. Rendering from an arbitrary viewpoint in a 360 degree circle around the center of a tree is achieved by blending between the nearest two slicings. In our implementation, only 6 slicings with 5 slices each are sufficient to visualize a tree for a moving or stationary observer with the perceptually similar quality as the original model.Item Visibility Complexity of a Region in Flatland(Eurographics Association, 2000) Rigau, Jaume; Feixas, Miquel; Sbert, MateuThe aim of this paper is to study the visibility complexity of different regions in a 2D scene. Based on mutual information, which we used in our previous work to define scene complexity, we propose two measures that quantify the complexity of a region from two different points of view. The knowledge of the complexity of a region can be useful to determine how difficult it is to recompute the visibility links for an animation depending on the regions visited or to obtain the complexity of the movement of a robot. We also envisage its applicability to obtain an optimal load balancing in a parallel computation by dividing the geometry in equal complexity regions.